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How Aztecs Played Their Rubber Matches |
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Written by Xiuhcoatl
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Nov 24, 2005 at 03:17 AM |
How Aztecs Played Their Rubber Matches
Written by Erik Stokstad
Science
06/18/99
When 16th century Spanish clerics came to the New World, they were
enthralled by a fast-paced and sometimes bloody sport. Teams of up to
six athletes would whack heavy, solid balls through hoops several
meters above the stone courts using anything but their hands or feet.
Apart from the occasional postgame human sacrifice, what most
astonished the Spanish were the ricocheting balls. "I do not
understand," wrote Pedro Martyr, the official historian of the Spanish
court in 1530, "how when they hit the ground they are sent into the air
with incredible bounce." For Europeans used to playing with pigskins,
the rubber balls were practically miraculous.
The native Americans made their seemingly magical material, Martyr
wrote, by collecting sap from lowland trees and mixing in juice from a
vine. Four centuries later, this crude recipe has finally given up some
of its secrets. On page 1988, researchers describe how the Olmec, Maya,
and other ancient Mexican and Central American cultures turned raw
latex into rubber. This feat of chemistry, which converts the slippery
polymers in raw latex to a resilient structure, was not duplicated
until the mid-19th century. "It's a marvelous example of technology
demonstrated at an incredibly early stage," says Frank Bates, a polymer
chemist at the University of Minnesota, Minneapolis.
The ball game, invented at least 3400 years ago, was an important
ritual for many Mesoamerican societies. To the Maya, for instance, the
game--called chaah--reenacted portions of their creation story. By the
5th century A.D., many towns had central stone courts, some of which
could hold thousands of spectators. Leaders tested prophecies through
tournaments, rival cities took out their aggressions on the court, and
the rich placed huge wagers. According to a 16th century codex, the
Aztec capital Tenochtitlan demanded 16,000 rubber balls each year as
tribute from one province. The ballmakers "were the ancient equivalent
of Rawlings," the sporting goods manufacturer, says Warren Hill, an
archaeologist at the New World Archaeological Foundation of Brigham
Young University in Provo, Utah. These societies also used rubber for a
host of other products, including religious figurines, incense, and
even lip balm.
Last summer, Massachusetts Institute of Technology (MIT) archaeologist
Dorothy Hosler and undergrad Michael Tarkanian traveled to Chiapas,
Mexico, to gather the raw materials for rubbermaking mentioned in
ancient documents. To their surprise, they saw farmers collecting latex
by slashing the bark of Castilla elastica trees, then mixing in juice
from pulverized morning glory vines that wrap around the trees--just as
the 400-year-old texts described. "It was amazing," recalls Tarkanian.
"After about 10 minutes, a mass of rubber rose to the surface. We
formed it into a ball that would easily bounce over your head."
The pair brought the ball, as well as raw latex and vine juice, back to
their lab. A battery of tests showed that the homemade rubber was about
twice as elastic as dried latex, which cracks when handled. With MIT
materials scientist Sandra Burkett, the researchers probed the material
with nuclear magnetic resonance spectroscopy, finding unidentified
organic compounds in the latex that were absent from the rubber.
The team speculates that some of these mysterious compounds might be
plasticizers, which would keep the latex runny by preventing its
polymer molecules from linking to each other. (Modern rubber is made by
cross-linking polymers.) If the vine juice dissolves the plasticizers,
the researchers thought, polymer molecules would be more likely to
entangle and form a rubbery mass. Although they failed to find direct
evidence for cross-linking, they did discover vine juice
components--traces of sulfonyl chlorides and sulfonic acids--that can
react with polymers, stiffening segments and making them more likely to
interact. The team says that only a few such entanglements would be
enough to give the rubber its spring.
Understanding ancient rubbermaking "teaches us how conscious these
people were of their environment and how they were able to manipulate
it," Hosler says. She and her colleagues next plan to test rubber made
with varying amounts of vine juice to see whether the Olmec, Maya, and
Aztec could have engineered rubber with specific elasticities. No
matter what they find, the Mesoamericans have earned the respect of
modern chemists. "To discover [the process] and refine it to make those
products is impressive," says Bates. "They probably had a pretty good
R&D team."
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History 